This invention relates to a piezoelectric audio transducer, such as a microphone.
Piezoelectric microphones suited for underwater use are known. For example, in U.S. Pat. No. 5,218,576 to De Chico a piezoelectric microphone has a piezoceramic transduction layer and a metal substrate with a thin film of viscous fluid between them. The viscous film allows the transduction layer and substrate to expand and contract relative to each other when the laminate bends under increasing hydrostatic pressure as the transducer descends in a body of water. While this arrangement reduces hydrostatic stresses, such stresses are not eliminated.
U.S. Pat. No. 4,013,992 to Bewberry et al. describes a microphone intending to expose both sides of the piezoelectric ceramic plate to ambient pressure. This would tend to avoid bending under increased hydrostatic pressure. However, it is believed that the design may be improved.
Accordingly, the present invention seeks to provide an improved piezoelectric audio transducer.
A piezoelectric audio transducer suitable for underwater use comprises a piezoelectric ceramic plate within a housing having open front face and back faces exposing the front and back faces of the ceramic plate to ambient pressure. The ceramic plate can be supported in spaced relation from the housing by, for example, open cell foam, so as to be vibrationally isolated from the housing.
According to the invention, there is provided, a piezoelectric audio transducer comprising: a piezoelectric ceramic plate; a housing for said ceramic plate, said housing having an open front face exposing a front face of said ceramic plate to ambient pressure and an open back face exposing a back face of said ceramic plate to ambient pressure.